A strong earthquake with a magnitude of 6.1 jolted northern Japan on Monday, the US Geological Survey said, but there was no immediate reports of damage or casualties.
The undersea quake struck at 8:30 pm (1130 GMT) off the east coast of Japan's main island of Honshu, at a depth of 33 kilometres (20 miles).
The epicentre was located about 100 kilometres east of the city of Iwaki.
Two hours earlier, a quake with a magnitude of 5.0 hit the same area, the USGS said. The Japan Meteorological Agency
put the magnitude of the earlier quake at 5.2.
The earlier quake did not trigger a tsunami warning and there were no reports of casualties or damage.
Japan experiences 20 percent of the world's major earthquakes. A powerful inland quake in the north of the country on June 13 triggered landslides and killed 12 people.